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Running Linux at 320x200 15kHz on a CRT reference monitor?

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First post, by Zilch

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Hi all,

I'm really considering getting a CRT for some gaming schtuff. A friend of mine is selling a JVC BM-1400PN-A.

It seems to be a pretty decent unit. Accepting of resolutions such as 240P and 480I.

My problem is this... I'd really like to run some older games on it, but I don't really have any retro hardware. Fortunately, I have a PC with VGA output that I could maybe use...

Doing some research showed that I can use this tool to set my Linux output resolution to 320x240P @ 15kHz - which should work with the JVC.

After that, I can get some some resistors and stuff to combine the separate H and V sync into one sync, and send the RGB signals straight to the monitor with 75 ohm load on. The monitor does appear to support YUV RGB input with separate sync.

In theory this is reasonably sound - but as all good theories go, there's always a catch!

Let me know what you think? Hopefully this works.... ?

EDIT... fixed the YUV thing

Last edited by Zilch on 2023-08-23, 11:25. Edited 2 times in total.

Reply 1 of 3, by mkarcher

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If the card sends RGB and the monitor expects YUV, all colors will be completely wrong, but this can be worked around in software, unless U and V require actual negative voltages to access all colors. The VGA RAMDAC is unable to provide negative voltages on either R, G or B.

Reply 3 of 3, by Zilch

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So doing some more research it seem that an input signal any higher than 15kHz may cause permanent damage to the monitor. Reason for this is because normally it still outputs at 31kHz before loading the drivers.

I'm not sure if this could be fixed using a passive low pass filter?

EDIT: Will be messing around a bit later. I think I may be able to create a simple active low pass filter using an NE5532 or whatever op amp I can manage to find.

Thankfully I know someone with an oscilloscope, so I can be 100% it will not mess up the monitor.

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